1. Field of the invention
The present invention relates to a conveyance apparatus for a continuous form printed by a printing machine, particularly the present invention relates to a conveyance apparatus for a continuous form, having sprocket holes on both edges thereof, carried at a constant speed by a rotating tractor such as a sprocket, a pin roller (a roller having pins planted with equal interval on the edge thereof), or a pin belt, to feed the continuous form printed by a printing machine to an after-treatment machine by using carrier rollers.
2. Description of the Related Art
In recent years, high-speed printing machines for printing data output, from a network of small computers or from a single large computer, on a continuous form is utilized for making individual forms or individual business reports.
High-speed printing machines for continuous forms and a conveyance of the continuous form are disclosed in japanese patent application numbers (KOKAI) S49-5229, S57-158869, and H4-51182.
An example of the structure of a conventional high-speed printing system PS is shown in FIG. 1. The conventional printing system PS includes a high-speed printing machine PM to print on the continuous form 9, and an after-treatment machine AM to conduct an after-treatment on the printed continuous form 9 such as cutting thereof or separation thereof in accordance with the type of printing thereon.
The printing machine PM in this example uses the technology of an electrophotography, so that it Lncludes a continuous form stock 1, a printing unit 2 having a photoreceptor drum 3, a pin roller 4, a fixing unit 5, conveyance rollers 6, a pair of ejection rollers 7, an end sensor 8, and a control unit 10. The after-treatment machine AM includes a pair of drawing rollers 11, a pair of cutters 12 for cutting the continuous form 9, a stacker 13, a movable carriage 14, and two pairs of conveyance rollers 15.
In the printing machine PM, the rotating photoreceptor drum 3 is electrically charged and a latent image is formed on the photoreceptor drum 3 by a laser beam transmitted from the optical unit (not shown). This latent image is developed by toner and a toner image is formed on the photoreceptor drum 3. Then the toner image on the photoreceptor drum 3 is transferred onto the continuous form 9 fed to the rotating photoreceptor drum 3 at the same speed as the rotational speed thereof, and high-speed printing is realized.
FIG. 2 shows the continuous form 9 to be printed by the high-speed printing machine PM in FIG. 1. As shown in FIG. 2, there are provided series of holes hereinafter sprocket holes) 91 on both edges of the continuous form 9. The distance between the sprocket holes 91 is the same as the distance between the pins 41 on the pin roller 4 in FIG. 1. The continuous form 9 is conveyed by the pin roller 4 by its sprocket holes 91 engaged with pins 41. Since the rotational speed of the pin roller 4 is the same as that of the photoreceptor drum 3, the conveyance speed of the continuous form 9 is exactly the same as the peripheral speed of the photoreceptor drum 3.
As shown in FIG. 1, there is provided a fixing unit 5 for fixing the toner on the continuous form 9 at the downstream side of the printing unit 2, a pair of ejection rollers 7 at the downstream side of the fixing unit 5, and conveyance rollers 6 between the printing unit 2 and the ejection rollers 7. The ejection rollers 7 pinch the continuous form 9 and rotate a little faster than the rotational speed of the pin roller 4 to input tension to the continuous form 9 between the printing unit 2 and the ejection rollers 7 where the fixing unit 5 is located.
In other words, the ejection rollers 7 have a faster peripheral speed than the conveyance speed of the continuous form 9 conveyed by the pin roller 4 when the ejection rollers are not ejecting paper. However, the rotational speed of the ejection rollers 7 is reduced when the continuous form 9 is engaged with the pin roller 4, since the peripheral speed of the pin roller 4 is lower than the peripheral speed of the ejection rollers 7. The torque produced by the ejection rollers 7 is changed to tension on the continuous form 9 between the printing unit 2 and the ejection rollers 7. The ejection rollers 7 pinching the continuous form 9 slip on the surface thereof.
The continuous form 9 is pulled into the after-treatment machine AM by the drawing rollers 11 and conveyed by the conveyance rollers 15. The continuous form 9 is folded and is piled in the stacker 13. The pair of cutters 12 are located between the two pairs of conveyance rollers 15 facing each other and cut the continuous form 9 at the change of the substance of the print. When the continuous form 9 is cut, it will become a sheaf of papers and will be stacked on the movable carriage 14 separatably as shown in FIG. 1.
The cutters 12 are activated, synchronously with the printing speed on the continuous form 9 at the photoreceptor drum 3, to cut the continuous form 9. The drawing rollers pull in the continuous form 9 at the conveyance speed thereof by the pin roller 4. That is, the continuous form 9 is after-treated in the after-treatment machine AM at the printing speed of the printing unit 2 in the printing machine PM.
However, above-described printing system PS has a frequently occurring problem at the end of the continuous form 9. Precisely, during normal printing, the continuous form 9 is pulled by the pin roller 4 rotating at the constant speed and the reduced peripheral speed of the ejection rollers 7 is to the peripheral speed of the pin roller 4, but the peripheral speed of the ejection rollers is increased when the continuous form 9 is disengaged from the pin roller 4. Accordingly, the speed of the continuous form 9 through the ejection rollers 7 is suddenly increased, though the conveyance speed of the continuous form 9 in the after-treatment machine AM is not changed from the conveyance speed of the pin roller 4. As a result, the continuous form 9 is jammed into the drawing rollers 11, and various problems may occur, such as the continuous form 9 is pulled by the drawing rollers 11 in a twisted or a folded condition, the continuous form 9 jams in the after-treatment machine AM, or the continuous form 9 is irregularly cut by the cutters 12.